Embodiments herein generally relate to printing systems (e.g., electrostatographic printing systems) and associated printing methods. More particularly, the embodiments relate to a system and a method for gradually adjusting a look-up table (LUT) for a print engine in order to improve the regulation of color quality of printed images.
Generally, in order to print an image having a desired color a printing system will use a look-up table (LUT) that is representative of a tone reproduction curve for its print engine. Such an LUT is unique to the print engine and correlates target values for a color (e.g., target tone values) with digital input values (e.g., halftone dot area coverage amounts expressed, for example, in terms of levels, ratios or percentages) that will achieve those target values. Unfortunately, with time and use, the tone reproduction curve drifts causing the LUT to become less accurate such that the digital input values no longer achieve the target values. Changes in the tone reproduction curve are typically monitored by periodically generating and evaluating test images (i.e., test patches) to identify differences between target values for a particular color and actually achieved values. Once identified, various different techniques can be used alone and/or in combination to compensate for these differences. For example, various physical actuators within the printing system may be selectively adjusted in order to alter specific printing parameters, such as developer bias, charge level, etc. and, thereby to compensate for changes to the tone reproduction curve. Additionally or alternatively, the LUT for the tone reproduction curve can be updated. However, when there is a significant difference between a target value for a color and the actually achieved value, as is often the case when there is an extended period of time between monitoring operations, the above-described compensation techniques can result in a sudden and visually perceivable (i.e., noticeable) color correction. Such visually perceivable or noticeable color corrections are generally objectionable to customers, particularly, if they occur mid-image or mid-document.
The following documents, which are all assigned to Xerox Corporation of Norwalk, Conn., USA, relate to the regulation of color quality in printed images and are incorporated herein in their entirety by reference: U.S. Pat. No. 5,347,369 issued to Harrington on Sep. 13, 1994; U.S. Pat. No. 5,748,330 issued to Wang et al. on May 5, 1998; U.S. Pat. No. 6,694,109 issued to Donaldson et al. on Feb. 17, 2004; U.S. Pat. No. 7,239,819 issued to Gross et al. on Jul. 3, 2007; U.S. Patent Application Publication No. 2009/0153911 filed by He et al. on Jun. 18, 2009; and U.S. Patent Application Publication No. 2010/0054769 filed by Adiletta et al. on Jul. 15, 2009.